An electric drivetrain of the aforementioned type is known. Such an electric drivetrain includes a synchronous electric machine comprising an electrically powered stator and rotor, as well as a variable frequency converter of the load-commutated converter type, connected to the stator of the electric machine. The variable frequency converter comprises a bridge rectifier of thyristors designed to be connected to an incoming three-phase electrical grid and a bridge inverter of thyristors connected on the output side of the rectifier. The incoming electrical grid is produced by an upstream electrical unit made up of a combination of gas turbines and electric generators. The thyristors of the inverter are guided by inverter restraint, whereas those of the bridge rectifier regulate the current. The variable frequency converter thus provides a source of current, able to power the stator of the synchronous electric machine.
However, such an electric drivetrain generates, both on the side of the incoming electrical grid and the side of the synchronous electric machine, harmonic currents of a frequency equal to an uneven multiple of the frequency of the primary current, this uneven multiple not being a multiple of 3. These harmonic currents give rise to coupled harmonics being applied along the downstream drive line of the gas compression device, and on the upstream drive line of the turbines producing the input electrical grid. These coupled harmonics are likely to energize the resonance frequency of this equipment, which can lead to its deterioration, even its destruction.
Moreover, such a drivetrain likewise generates inter-harmonic currents, both on the side of the input electrical grid and the side of the synchronous electric machine. These inter-harmonic currents give rise to cogging, which is likely to energize the frequencies of the very modes of the upstream and downstream drive lines and thus damage these lines.
In addition, such a drivetrain requires using a dedicated electric power supply for the rotor of the electric machine, said electric power supply requiring a high number of individual components. Some of these components are, for example, diodes mounted on the rotor. Because of the significant mechanical constraints applied to these “rotating” diodes, they present reliability problems. This decreases the reliability of the drivetrain unit and creates high manufacturing and maintenance costs.